Upon submitting an order in "MarketPress", the page goes blank!

At the final stage of an order, the page goes blank!
Opera shows an error message as seen in the attached file while Firefox, Safari, etc show blank page. Refreshing the blank page the URL stay the same ...../checkout , while the blue message says, "Oops! Looks like you haven't added anything your cart. Let's go shopping!"
Checking the orders in the back-end, all orders are listed there!
Please advice,
It is a kind of urgent as this is a live production site, appreciate a quick respond :slight_smile:
Thanks :slight_smile: